This invention relates to a transmission and in particular, to a continuously, variable transmission for varying an output drive ratio between a minimum and maximum value.
Transmissions for vehicles and also used in most other environments generally have a single set gear ratio or the ability to select a number of gear ratios either automatically or by manipulation of a gear stick.
Continuously variable transmissions are also known and generally comprise belt systems in which the effective diameter of a pulley about which a belt is driven changes so as to change the gear ratio of the transmission. Other continuously variable transmissions include ridged body systems in which levers, pawls or gears are mounted on an eccentric and by changing the amount of eccentricity the drive ratio of the system can be altered between minimum and maximum ratios.
The object of the preset invention is to provide a improved transmission which has applications from heavy duty environments such as in vehicles to more refined environments such as transmitting power from relatively small electric motors.
The invention may be said to reside in a transmission, including;
a gear system including an output gear for supplying output rotary power and a control gear for controlling a drive ratio of the gear system dependant on the speed of movement of the control gear; and
momentum control means coupled to the control gear for transferring momentum to and from the control gear to change the speed of movement of the control gear to, in turn, change the drive ratio of the transmission.
The transmission according to this invention has applications in heavy duty environment such as vehicles and also in, some forms, in more refined environments such as electric motors.
In one embodiment the momentum control means is a momentum conversion means xe2x80x9closesxe2x80x9d or dissipates the momentum from the control gear in order to change its speed, and thus loses energy from the system. In this embodiment of the invention the transmission includes a brake mechanism for slowing down or allowing speed up of the control gear so as to change its speed to, in turn, change the drive ratio of the transmission.
In one aspect of this embodiment the brake means can include an electromagnetic or magnetic brake which changes the speed of the control gear by magnetic or electromagnetic force.
This embodiment may include a fly wheel coupled to the control gear, the fly wheel forming a housing in which is located a magnetic fluid, a brake member in the housing, and a moveable magnet displaceable towards and away from the housing so as to cause the magnetic fluid to change its viscosity to apply a braking force to the fly wheel to change its speed.
In a second embodiment the momentum control is a momentum transformation means which is a substantially conservative momentum control. In this embodiment momentum is transformed from one state to another
In this embodiment the momentum control includes a mass moveably coupled to the control gear for movement between first and second positions so as to change the moment of inertia of the mass and to, in turn, change the moment of inertia of the control gear to change the speed of the control gear as the mass moves between the first and second positions.
Preferably the control gear is coupled to a control shaft and the mass is mounted on the control shaft for radial movement with respect to the control shaft so that when rotary power is supplied to the transmission the control shaft is rotated and as the speed of rotation of the control shaft changes centrifugal force applied to the mass causes the mass to move radially outwards to change the moment of inertia so as to change the speed of the control shaft and, in turn, change the speed of the control gear.
In the first embodiment of the invention the gear system is most preferably an orbital gear system in which the output gear is an internally toothed gear and the control gear is an externally toothed gear, the control gear being mounted for orbital motion so as to transmit drive to the output gear.
In the second embodiment of the invention the system most preferably comprises a planetary orbital spur gear system.
Preferably the planetary orbital spur gear system includes;
the output gear mounted on an output shaft;
a planet cage;
at least one spur cluster carried by the cage, the spur cluster having a first planet gear in mesh with the output gear, and a second planet gear fixed for rotation with the first planet gear; and
an idler gear in mesh with the second plant gear and also in mesh with the control gear.
This arrangement has particular advantages in that the system is a fully external tooth gear system rather than requiring at least one gear with internal teeth as is the case with most planet systems, and the idler gear enables the rotation of the output gear and the control gear to occur in the same direction and also provides the ability to conveniently set the gear ratio of the system at a desired gear by simply selecting the appropriate teeth ratio between the output gear, the first planet gear, the second planet gear and the control gear. This is contrary to normal planet systems in which it is necessary to maintain the teeth ratio within very specific limits to ensure correct meshing of teeth thereby reducing the range of gear ratios which can generally be obtained and which are set in the planet gear system.
In a third embodiment of the of the invention the momentum control means includes;
a fly wheel coupled to the control gear;
a brake mechanism having movable brake arms carried by the gear system so that as the speed of rotation of the gear system increases the brake arms pivot under centrifugal force to engage the fly wheel and drag the fly wheel so as to change the speed of the control gear to in turn change the drive ratio of the transmission.
Preferably the control shaft in this embodiment of the invention also includes a ratchet ring for engaging a pawl so as to prevent backward rotation of the control shaft thereby placing the transmission into a low gear without allowing the control shaft to place the transmission into neutral gear.
The invention may also be said to reside in a planetary orbital spur gear system including;
a planet cage;
at least one spur cluster coupled to the planet cage and including a first planet gear and a second planet gear fixed for rotation with the first planet gear;
an output gear coupled to the first planet gear for supplying rotary power; and
a control gear mounted for rotation relative to the output gear and coupled to the second planet gear for controlling the drive ratio of the system.
This arrangement has particular advantages because all of the gears in the system can be externally toothed gears and an internally toothed gear is not required.
Preferably the second planet gear is coupled to the control gear by an idler gear.
This arrangement provides additional advantages in that the gear ratio of the transmission can be initially set at a particular drive ratio when the planet cage and output gear rotate at the same speed by suitable selection of the tooth ratio between the control gear, the first planet, the second planet gear and the output gear. Thus, a wide range of gear ratio are available with the orbital spur system in contradistinction to normal planet systems in which the very limited range is possible.
Preferably the drive ratio of the transmission is altered between maximum and minimum limits by varying the speed of the control gear relative to the cage so as to control the spur cluster to, in turn, control the speed of the output gear.
Preferably the control gear is coupled to a control shaft and the system includes means coupled to the control shaft for controlling the speed of rotation of the control shaft and therefore the control gear to, in turn, control the drive ratio of the transmission.
A further aspect of the invention may be said to reside in a transmission, including;
a gear system including an output gear for supplying output rotary power and a control gear for controlling a drive ratio of the gear system dependent on the speed of movement of the control gear; and
magnetic or electromagnetic brake means for controlling the speed of rotation of the control gear to, in turn, set the drive ratio of the transmission.
This aspect of the invention has particular advantages in that the magnetic or electromagnetic brake will not fade. Thus if the transmission is to be set at a particular drive ratio for lengthy periods of time in which the brake is required to control the speed of the control gear to a particular rotational speed then the brake system will not fade and the gear ratio can be controlled accurately over that lengthy period of time. If mechanical brake systems employing a frictional surface are used then the frictional contact between components of the mechanical brake system will wear causing a slight fading of the brake and therefore of the braking force applied to control gear. Thus the speed of control gear can change slightly notwithstanding the application of the brake which can change the drive the ratio from the required over a length period of time.